The measuring system is used in a liquid collecting apparatus, for example. The liquid collecting apparatus will be described taking a blood collecting apparatus which collects blood, for example. The blood collecting apparatus is used for quantitative analysis in nuclear medicine diagnosis (e.g. PET (Positron Emission Tomography), SPECT (Single Photon Emission CT) and so on), and are used especially for measurement of a radioactive concentration in arterial blood of small animals (e.g. mice, rats and so on). Conventionally, the following modes (a)-(d) are employed in the above quantitative analysis of small animals:
(a) Manual Blood Collection
Blood delivering itself under blood pressure from the other end of a catheter inserted into a mouse artery is received in a suitable receptacle. Then, a fixed volume of the blood in the receptacle is sucked up with a volumetric pipette, and a radioactive concentration in the whole blood is measured by calculating (i.e. counting) radiation in the sucked-up blood. Further, plasma is obtained by centrifugal separation of the blood remaining in the receptacle, which is similarly collected with a volumetric pipette to measure a radioactive concentration in plasma.
(b) Artery Channel β-Ray Detector
A β+ ray detector is installed in an arterial blood channel to measure a radioactive concentration in blood. β+ rays are detected with a plastic scintillator or PIN diode. In Nonpatent Document 1, for example, a diode has a long and thin shape with a length of 30 [mm], and a detectable area is increased by installing a tube containing blood along the direction of a long side, thereby to secure detection efficiency.
(c) Microfluidic Device Mode
This is a mode which, as shown in FIG. 15, leads arterial blood delivering itself under mouse blood pressure onto a microchip (device) MC. The microchip MC has, arranged thereon, one main flow path FM, selectable branch flow paths FB, and side flow paths FN for feeding a mixed liquid H of heparin solution and physiological saline used for flow path cleaning or blood discharging, and for draining used mixed liquid H of heparin solution and physiological saline and blood B. A receptacle is placed at the end of each branch flow path FB, and one of the branch flow paths FB is selected by a gas pressure of argon gas Gas supplied to the microchip MC or a mechanism of the microchip MC. With one of the branch flow paths FB selected, blood B is poured in. The flow velocity of the blood B and the mixed liquid H of heparin solution and physiological saline is increased by placing the interior of each branch flow path of the microchip MC at negative pressure, and further installing a peristaltic pump. Each of the flow paths FM and FB is formed by grooving the microchip MC in a predetermined size. It is the characteristic of the microchip MC that a minute volume of blood B is specified if a groove length or a groove area of the poured-in blood B is known. With the blood B of a predetermined volume filling the flow paths, based on the specified minute volume, the blood B is sent along with the mixed liquid H of heparin solution and physiological saline into a predetermined receptacle (not shown) by feeding the mixed liquid H of heparin solution and physiological saline under pressure. Subsequently, each of the flow paths FM and FB is cleaned with the mixed liquid H of heparin solution and physiological saline to be ready for a next blood collection. The blood B in the receptacle is washed out along with the physiological saline into another receptacle, and the radiation in the blood B is counted with a well counter (see Nonpatent Documents 2 and 3, and Patent Document 1, for example).
(d) Radioactivity Time Variation Measurement from PET Images
This is a technique which sets an area of interest to the left ventricle of PET dynamic images acquired, and determining time variations of radioactive concentration in the area (see Nonpatent Document 4, for example).
However, when the above techniques are applied to radioactivity measurement in arterial blood of small animals, there arise the following problems.
(a) Manual Blood Collection
In the case of manual blood collection, it is possible to determine accurately a radioactive concentration in the whole blood from the blood obtained, and also a radioactive concentration in plasma from the plasma resulting from centrifugal separation. However, the question of the operator's procedure imposes restrictions to blood collecting intervals, and it is impossible to acquire data of rapid variations (in the order of several seconds) in the radioactive concentration occurring immediately after medication. Further, since a large amount of blood is collected at a time, the number of times of blood collection is limited in order to avoid the small animals dying from loss of blood.
(b) Artery Channel β-Ray Detector
It is possible to track minute time variations in the radioactive concentration in the whole blood through the tube by which arterial blood flows through the β+ ray detector. However, it is impossible to acquire a radioactive concentration in plasma which serves as the input function for quantitative analysis model.
(c) Microfluidic Device Mode
This mode can track minute time variations in the radioactive concentration in a slight amount of blood. Although data of collected blood is washed out to a separate receptacle, there is no function to put it to centrifugal separation to acquire a radioactive concentration in plasma which serves as the input function for quantitative analysis model.
(d) Radioactivity Time Variation Measurement from PET Images
This mode can obtain only time variations in whole blood radioactive concentration. Further, in the operation to set the area of interest to the left ventricle, quantification of the radioactive concentration obtained from the left ventricle is impaired due to a partial volume effect from tissues surrounding the left ventricle. There are also problems that specifying the left ventricle is not easy particularly with a small individual such as a mouse, and that it is also difficult, with medication inducing a high degree of accumulation in tissues around the heart, to set the area of interest to the left ventricle without anatomical information.
So, in order to solve these problems, there is provided a flow path through which a liquid (e.g. blood) to be measured flows, with an extracting device provided in an intermediate position of the flow path to insert a gas or a liquid other than the liquid to be measured, as separators, at designated predetermined intervals, thereby to take out the liquid to be measured, as separated in the time series (see Patent Document 2, for example). In this Patent Document 2, the liquid can be taken out in minute volumes of about 1 [μL], for example, by inserting the separators consisting of the gas or liquid while continuously feeding the liquid to be measured into the flow path. And consumption of the liquid to be measured accompanying a cleaning liquid (heparin solution in the case of blood collection) for every collection as in the prior art can be held down, and the amount of collected liquid can be minimized. Since the operation to insert the separators is excellent in speed, repeated collection in a short time, i.e. frequency of collection, can be secured. As a result, the amount of collected liquid can be reduced, and the frequency of collection can be secured. Where the liquid to be measured is blood, the amount of collected blood can be reduced, and the frequency of blood collection can be secured.
Further, where the liquid to be measured is blood, the blood is put to centrifugal separation, and the radiation included in plasma and blood cell resulting from plasma separation is separately counted. Therefore, the radioactive concentration in plasma can be measured.